Clay is found most frequently in flat rolling land where there has been prolonged weathering but little erosion. Forming a sticky, poor-draining soil that is the bane of many gardeners, it consists of rock that has been weathered into very small particles – a teaspoonful of the clay mineral allophane has the surface area of a rugby field. The small size and flatness of the particles is what makes clay impermeable.
Clay has a unique property that has been exploited for thousands of years. When it is fired under high temperatures the particles cement together to form the hardened waterproof material used in pottery.
Māori did not fire clay, but they were well aware of it through their cultivation of the soil. There were over 30 Māori terms for different clays, soils and gravels.
When Okurarenga pā at Māhia Peninsula was besieged by a combined force of tribes armed with muskets, the inhabitants began to starve. After three months they had to resort to eating a soapy clay known as uku. The place was given the name Kaiuku, ‘to eat clay’.
Some of the earliest European settlers used clay to make wattle and daub dwellings, and sod or cob houses and fences. Chimneys were made from tree fern trunks heavily plastered with clay. Māori also began to use sod to build whare paruparu (dirt houses) and walls known as takitaki.
In 1881, to stimulate local industry, the government offered £250 for the production of £1,000 worth of earthenware products. A Dunedin company won the grant and by 1887 other pottery works were producing bricks, drainpipes, chimney pots and tiles, as well as porcelain and terracotta products.
European settlers dug small clay pits, and toiled at the back-breaking task of shovelling the puggy soil. Kilns were built to fire the clay. New Zealand farms, often essentially wetlands, soon had kilometres of drainage pipes.
During the late 1800s and early 1900s brickworks appeared, with their chimney stacks and large bottle kilns – wide at the bottom and tapering upwards like the neck of a bottle. The kilns churned out red bricks by the thousand, helping to build the growing townships. The colour of bricks and roofing tiles varies according to the local clay. Banks Peninsula bricks made from clay-rich loess, a fine, wind-blown sediment found in Canterbury, are a distinctive tan colour.